1. Field of the Invention:
This invention relates to a structure for mounting on a vehicle body a suspension member, with which a suspension arm and other parts of a suspension of a vehicle are connected.
2. Description of the Prior Art:
There is the case where a suspension member, with which a suspension arm and other parts constituting a suspension of a vehicle are connected, is mounted on a vehicle body through cushion mounts disposed in predetermined positions (for example, Japanese Utility Model Public disclosure (KOKAI) No. 61-59108).
The suspension member as noted above is formed into an approximately rectangular or H-shaped contour in plan, as shown in FIGS. 9 and 10, which is connected to a vehicle body 21 on four corners, or formed into an approximately triangular shape in plan, as shown in FIGS. 11 and 12, which is connected to the vehicle body 21 on three corners.
In the suspension member 20 shown in FIGS. 9 and 10, left and right suspension arms 26, 28 each supporting a wheel 24 are connected with both sides of the suspension member 20. The suspension member 20, with which the suspension arms are connected, is mounted to the vehicle body 21 through two cushion mounts 30 on two corners in front of a rotary axis of wheels 24 and through two cushion mounts 32 on two corners in the rear of the rotary axis of the wheels 24.
In the suspension member 22 shown in FIG. 11, the left and right suspension arms 26,28 each supporting a wheel 24 are connected with both sides of the suspension member 22. The suspension member 22, with which the suspension arms are connected, is mounted to the vehicle body 21 on one corner in front of a rotary axis of the wheels 24 through one cushion mount 30 and on two corners in the rear of the rotary axis of the wheels 24 through two cushion mounts 32. The suspension member 22 shown in FIG. 12 is mounted to the vehicle body 21 on two corners in front of the rotary axis of the wheels 24 through two cushion mounts 30 and on one corner in the rear of the rotary axis of the wheels 24 through one cushion mount 32.
In either of the suspension members as noted above, each cushion mount is made of rubber into the form of a cylinder and disposed so as to extend an axis thereof in a vertical direction of the vehicle body. Thus, the suspension member is mounted to the vehicle body by bolts and other connecting means extending vertically through the cushion mounts.
When a vehicle, on which the suspension member as noted above is mounted, travels, as shown in FIGS. 9-12, lateral force F.sub.1, yawing force F.sub.2 intending to move the vehicle body around a vertical line passing through the center of gravity of the vehicle, longitudinal force F.sub.3 such as driving force or braking force, vertical force F.sub.4 due to the action of a differential gear or the like and other forces act on the suspension member and further act on the cushion mounts attached to the suspension member.
Now, each of the cushion mounts of the vehicle should be set to ensure controllability, while reducing noises and vibrations so as to maintain satisfactory ride comfort. Generally, it is assumed that the spring constants or rigidities of the cushion mount in the longitudinal and vertical directions of the vehicle are preferably set to be small from a view point of improving the ride comfort and the rigidity in the left and right directions (lateral direction) is preferably set to be large from a view point of ensuring the controllability.
Then, in the cushion mount 30(32) having the axis set in the vertical direction of the vehicle, as shown in FIG. 8, for example, a pair of slots 31b are provided to sandwich a central hole 31a formed in the cylindrical rubber, while a pair of inserts 31d made of hard material are embedded in a columnar portion 31c having no slot to form the cushion mount. The cushion mount is attached to the suspension member such that the pair of slots 31b are located longitudinally of the vehicle body and the suspension member is mounted to the vehicle body by a bolt extending vertically through the hole 31a.
When the suspension member receives the yawing force or torsional force in turning, the columnar portion 31c of the cushion mount is displaced in substantially longitudinal direction orthogonal to the axis thereof depending upon the amount of force thus received, so that it is liable to occur the buckling of the cushion mount by the lateral force and the rigidity in the lateral direction may be abruptly reduced. In order to cope with this while the lateral rigidity of the cushion mount has to be increased correspondingly in consideration of the rigidity reduction, the increase of the lateral rigidity is limited merely by the method of providing the inserts. Thus, the rigidity of rubber itself needs to be increased. However, the increase of the rigidity of rubber itself increases necessarily the longitudinal rigidity to thereby degrade the ride comfort.
All cushion mounts of the suspension member are considered to be disposed with the axes of the cushion mounts being directed longitudinally as disclosed in Japanese Utility Model Public Disclosure (KOKAI) No. 60-55508 for example. When the suspension member having the cushion mounts disposed in this manner receives the yawing force or torsional force in turning, the columnar portion of the cushion mount is subjected to the axial shear deformation while this columnar portion is not displaced in the vertical direction orthogonal to the axis. Accordingly, the reduction of the lateral rigidity of each cushion mount produced in the case where the cushion mounts are disposed with the axes directed vertically does not occur. In addition, it has been confirmed by inventors that when longitudinal shear deformation occurred in a cushion mount having the axis disposed longitudinally, the lateral rigidity of the cushion mount is increased, compared with that prior to occurrence of the shear deformation.
As mentioned above, when the cushion mount with upper and lower slots has the axis disposed longitudinally of the vehicle body, the lateral rigidity is not positively reduced by occurrence of the buckling of the columnar portion in turning and, on the contrary, the lateral rigidity is effectively increased, so that such disposition of the cushion mount is preferable to improve the controllability. On the other hand, as described in Public disclosure as noted above, in all cushion mounts having the respective axes disposed longitudinally, a load on the vehicle body acts always vertically on the cushion mounts. Therefore, when the slots are provided only in the upper and lower portions of each cushion mount and the load on the vehicle body is supported with the shear deformation of the columnar portion, the cushion mount is degraded in durability. Then, it is necessary that compressive deformation regions are provided in the connections between the columnar portion and a peripheral annular portion of the cushion mount to ensure the durability. However, by providing the compressive deformation regions, the vertical rigidity is increased and thus the function of compensating for the degradation of ride comfort with the slots is limited.